hstlnflw what is your location? what size home? you are replacing a 2 1/2 ton system? you are strictly all electric? how did old system perform both cooling and heating? any comfort issues? here are the performance/eff numbers from the AHRI HP Directory. according to the directory, the only matching system using the communicating air handler is the C01. and you should note the rather mediocre HSPF heating efficiency. The C04 air handler is not listed as a matching system. 3591483 Active Systems XL15I WEATHERTRON TRANE 4TWX5030A1 4TEE3C01A1 30200 12.50 15.00 29000 8.50 17600 1 HRCU-A-CB Also with the communicating air handler, you would want the matching XL900 communicating thermostat. I personally would forget the above configuration and go for the following. 1382160 Active Systems XL15I WEATHERTRON TRANE 4TWX5030A1 4TEE3F39A1 30000 13.00 15.75 30000 9.00 18000 your thermostat choices could be the 802,803, or HW VisionPro IAQ which is preferred. as to the heat strip, what size do you currently have? Trane offers a 7/12 KW and 10/15 KW staged modules. The idea that you might requirew a 19 KW seems extreme and not necessary. as far as price, nothing special here. I have seen three ton XL15i systems for about the same price. IMO Good Luck!

I will tell you upfront that my knowledge on the wiring aspect of HVAC is limited. With that said, you may consider calling a local professional referred to you by someone else to come out and get things working the way they should be for you. That's strange about the air handler, because the way I understand it, things should be wired as such: (thermostat)-->(air handler)-->(heat pump). Colors don't always mean anything, but usually orange is your reversing valve (terminal O). Your air handler should have a Y terminal.

You do not "need" a variable speed air handler. I have one. They are a premium item that is good at reducing humidity, properly configured, while providing superior comfort control. They are expensive, and should be matched to an appropriate heat pump and thermostat in order to get the most out of the system. But you don't "need" one. A standard air handler should work properly in any normal situation. What you really need is a tech that can properly diagnose your problem and communicate it to you in an understandable manner.

I am in agreement with everyone, the unit is old but as stated, was purchased by TRANE. However, the relays and other supporting parts are readily available. If I'm correct, I think Tigerdunes was pointing in the right direction. If you are not familiar with heating with heat pumps, then the air coming from the vents while in the heat pump mode alone, would feel cool to you. One thing you mentioned was that while it was in the heat pump mode, you did not measure voltage to the element. That would be normal. When the unit calls for AUX or Emerg. heat, then you would get a voltage to the heaters. Here's what I think is happening....the reversing valve is stuck...it was common on the older units. The unit stays in the cooling mode and when the first bank of heaters comes on, the cool air overcomes the full effect of the heater. Check the air coming from the outside unit. If it is warm and that will confirm the possibility of a stuck reversing valve. As mentioned also by Tigerdunes, replacing a reversing valve is expensive and given the age of your unit, whole replacement of the unit would be a better choice. Now a professional should be called however, I'll give you one thing you can try, if indeed it is still in the A/C mode. You can force the valve to slide into the heat mode by doing this.....disconnect the blower at the condenser. Turn the unit on in the heat pump mode and let it run....Given your temperatures, the condenser will slowly build pressure on one side of the valve as the pressure drops on the other side. You'll know you are getting close when you hear the compressor staring to load up. You'll suddenly hear a whoosh and the reversing valve has now reversed. Let it run for about a minute to make sure it has fully reversed. Shut the unit downand hook the fan back up. When the unit goes into the defrost mode, the valve may work and the unit defrosts but may not switch back to heat mode (sometimes they do, sometimes they don't.) If that's the case, you have to do it all over. This suggestion is just to get you some heat until you get someone out.